1. Field of the Invention
This invention relates to an improvement of a gear shift controlling device of an automatic transmission, particularly to a device of preventing contingent shift up when an accelerator pedal is released.
2. Description of the Prior Art
As a conventional gear shift control of an automatic transmission, the Japanese Patent Application Laying Open Gazette No. 62-220752, for example, discloses such control device that a gear shift diagram according to the vehicle speed and the opening of a throttle valve is stored beforehand and on the basis of such gear shift diagram, gear shift is automatically controlled in such a way that it is shifted up or shifted down to the gear shift stage corresponding to momentary speeds and openings of the throttle valve of a running vehicle or it maintains existing gear shift stage.
In the above conventional automatic gear shift control, however, we have such defects that even if an accelerator pedal is released and a throttle valve is closed, an engine brake refuses to work and contingent shift down occurs at re-accelerating after deceleration. More concretely, in the case where a gear shift diagram is stored as shown in FIG. 13, at the time of deceleration when an accelerator pedal is released so as to work an engine brake while a car is running by selecting the second gear at the point X in the figure, with the opening of the throttle valve becoming fully closed, working state of the engine in the gear shift diagram is shifted up to the third gear across the 2.fwdarw.3 gear shift line at the point Y in the figure and thus the engine brake refuses to work. In addition, when an accelerator pedal is stepped on and the opening of the throttle valve is increased so as to accelerate again after deceleration, working state of the engine is shifted down contingently to the second gear across the 2.rarw.3 gear shift line at the point K in the figure and accordingly, momentary lowering of driving force is caused and behaviour change of a vehicle body occurs, with the result that a driver is given an unpleasant feeling and car wheels becomes easy to slip, with bad influence upon running capacity of a car. These defects are especially conspicuous at the road where curves are continuous.
In order to avoid such unnecessary shift up at the time of deceleration running as mentioned above, in the Japanese Patent Application Laying Open Gazette No. 62-220750 it is so composed that, separately from the gear shift diagram set usually, another gear shift diagram for shifting gears on the basis of only the opening of the throttle valve is set and by controlling gear shift at the deceleration running on the basis of this gear shift diagram, sudden shift up at the time of deceleration running is avoided.
As another composition which solves the above problem, in U.S. patent application Ser. No. 384,714 (title of the invention: Control System for Automatic Transmission) filed on Jul. 25, 1989 by the present inventor, when the state requiring shift up at the speed lower than the vehicle speed set beforehand is detected, an output of shift up gear shift signal on the basis of this detection is delayed by the set time and if during this set time the state of deceleration running is reached (when the opening of the throttle valve is fully closed), the above output of shift up gear shift signal is released and no output is given. Thus, shift up at the time of deceleration running is avoided.
The present invention has for its object to prevent contingent shift up when an accelerator pedal is released and also subsequent contingent shift down when a pedal is stepped on and thus carry out a proper gear shift control.
In order to attain the above object, in the present invention it is so designed that when the engine braking with the accelerator pedal released is required, working state of the engine does not cross the shift up gear shift line according to the gear shift diagram.
Concretely, a solution to the problem by the present invention is premised on a gear shift controlling device of an automatic transmission whereby gear shift of the automatic transmission is controlled by the load on engine and the no. of revolutions (r.p.m.) of an engine driving system, such as vehicle speed. This device is provided with a load detecting means which detects load on engine and a signal change adjusting means which tempers the change of engine load signals which are detected by the load detecting means. This device also has a controlling means which receives outpus of the load detecting means and the signal change adjusting means and controls gear shift of the automatic transmission in such a way that gear shift is controlled according to the engine load signal and the r.p.m. of the engine driving system, on the basis of the engine load signal of the load detecting means when the engine load detected by the load detecting means increases and on the basis of the engine load signal for which signal change was tempered by the signal change adjusting means when the engine load detected by the load detecting means decreases.
Under the above composition, in the present invention at the time of acceleration when an accelerator pedal is stepped on and load on engine increases, actual engine load signal detected by the load detecting means is selected and therefore working state of the engine on the gear shift diagram changes according to actual change and thus usual automatic gear shift is obtained.
When a driver requires deceleration with an accelerator pedal released during running, an engine load signal which is tempered in change by the signal change adjusting means is selected and by this selection, working state of the engine on the gear shift diagram does not cross the shift up gear shift line as it is changing in downward direction toward the left side of the figure according to the decrease of r.p.m. of the engine driving system as shown in FIG. 12 and thus contingent shift up can be prevented.
After the above deceleration, when a driver steps on an accelerator pedal and the opening of the throttle valve increases, the engine load signal of the load detecting means is selected and working state of the engine on the gear shift diagram changes according to actual change and crosses the shift down gear shift line but since the shift up is prevented originally as mentioned above, no shift down occurs.
The object and novel features of the present invention will be understood more clearly by reading the following description, with reference to the accompanying drawings.